Compute InScopeSet in substInteractiveContext

Authored by niteria on Dec 26 2017, 6:28 AM.

Description

Compute InScopeSet in substInteractiveContext

It doesn't look like we keep any sets of free variables
of the types of Ids handy, so we just have to build them
when doing a substitution.

Test Plan: buildbot + run testsuite with debug

Reviewers: simonmar, simonpj, austin, bgamari

Reviewed By: simonpj

Subscribers: carter, rwbarton, thomie

GHC Trac Issues: Trac #11371

Differential Revision: https://phabricator.haskell.org/D3431